An electrodynamic-suspension (EDS) maglev, like JR's SCMaglev, drives current through onboard coils past a passive conducting guideway. The relative motion induces eddy currents in the guideway, which push back on the train with two components predicted by classic EDS theory:
F_lift = F0 · f² · v² / (v² + vc²)
F_drag = D0 · f · (v/vc) / (1 + (v/vc)²)
where f is the coil field fraction, v is train speed and vc (here 120 km/h) is the guideway's characteristic velocity set by its conductivity and pole pitch. Lift grows monotonically and saturates at high speed, which is why EDS trains need auxiliary wheels below their liftoff speed. Drag, by contrast, is largest near v = vc and falls off at both low and high speed — the classic eddy-current braking curve, visible in the force-vs-speed graph on the right.
The train levitates once F_lift exceeds its weight (mass × g, mass rising with passenger load). The levitation gap then follows the fractional excess of lift over weight, clamped to a realistic 8–150 mm band; propulsion power is drag force × speed plus the coil-excitation and housekeeping loads.
- Field strength — scales lift with f² and drag with f (more current, more induced eddy currents both ways).
- Target speed — the train eases toward this speed; drag peaks around 120 km/h then fades as v/vc grows.
- Passenger load — adds mass, raising the weight the lift force must overcome and the liftoff speed needed.